If you do a batch test with a staff and a offhand it doesn’t unequip the offhand when doing the staff run.
So it sims with staff + offhand in my combo sim, I should have lost 100 haste and 100 crit using the staff but I only lost 50 of each. Implying it didn’t take off my OH too for reference
Combo sim with results type
This is a single sim with only the staff - https://www.askmrrobot.com/wow/simulator/report/daf61238530e4b89aabbb1bf944cd891